Novel terpolymer containing styrene acrylonitrile and another acrylicmaterial

ABSTRACT

A TERPOLYMER COMPRISING A MAJOR AMOUNT OF STYRENE, AND MINOR AMOUNTS OF ACRYLONITRILE AND ANOTHER ACRYLIC MATERIAL SUCH AS ACRYLAMIDE, ACRYLIC ACID OR METHACRYLIC ACID IS DISCLOSED, WHICH HAS UTILITY AS AN ORGANIC PIGMENT IN PAPER COATING COMPOSITIONS. A STABLE AQUEOUS EMULSION OF THE TERPOLYMER IS PREPARED WITHOUT THE NEED FOR COMVENTIONAL PROTECTIVE COLLOIDS BY THE PROPER CHOICE OF EMULSIFIERS AND TEMPERATURE DURING AN EMULSION POLYMERIZATION PROCESS. THE AVERAGE PARTICLE SIZE OF THE TERPOLYMERS PRODUCED RANGES FROM ABOUT 0.1 TO ABOUT 0.2 MICRON.

United States Patent NOVEL TERPOLYMER CONTAINING STYRENE, ACRYLONITRILEAND ANOTHER ACRYLIC MATERIAL Denis K. Huang, Laurel, Md., assignor toWestvaco Corporation, New York, N.Y.

No Drawing. Original application Oct. 29, 1970, Ser. No. 843,240, nowPatent No. 3,595,823. Divided and this application Ian. 13, 1971, Ser.No. 106,233

Int. Cl. 1308f 15/40 US. Cl. 260-8013 2 Claims ABSTRACT OF THEDISCLOSURE A terpolymer comprising a major amount of styrene, and minoramounts of acrylonitrile and another acrylic material such asacrylamide, acrylic acid or methacrylic acid is disclosed, which hasutility as an organic pigment in paper coating compositions. A stableaqueous emulsion of the terpolymer is prepared without the need forconventional protective colloids by the proper choice of emulsifiers andtemperature during an emulsion polymerization process. The averageparticle size of the terpolymers produced ranges from about 0.1 to about0.2 micron.

BRIEF SUMMARY OF THE INVENTION This application is a division of thecopending application Ser. No. 843,240, filed July 18, 1969, now U.S.Pat. No. 3,595,823.

This invention relates to a novel terpolymer, to methods of preparingstable emulsions thereof, and to coating compositions containing thesame. The terpolymer comprises styrene as the major constituent, andacrylonitrile and an acrylic material such as acrylamide, acrylic acid,or methacrylic acid, as minor constituents. The new terpolymer findsgreat utility as a pigment in such things as paper coating compositions.

Polystyrene latices have been used for some time in floor polishes andpaint. In general, such non-film forming latices do not find use inpaper coating compositions because of poor pigment binding properties.Butadienestyrene, polyvinyl acetate, acrylic latices and the like havebeen used in paper coating compositions as filmforming binders, butthese latices, in conventional paper coating applications, have beenfound to be rather inadequate in providing the gloss and printabilitythat the ever-increasing packaging and printing standards demand.

According to the present invention, an economical nonfilm formingorganic terpolymer, comprising styrene as the major ingredient, can beprepared in the form of a stable aqueous emulsion. The terpolymer isuseful, for example, as an organic pigment in coating compositions. Thenovel terpolymer provides excellent gloss and ink holdout when used inprintability paper coating compositions as a coating pigment.Conventional paper coating binders can be used to bind the new organicpigment to the substrate. For example, the binder can be starch, proteinsuch as casein and alpha protein, or a synthetic binder such aspolyvinyl acetate, polyacrylates, and styrene-butadiene. In papercoatings according to the present invention, the binder makes up a minoramount of the coating composition, and the pigmentary component makes upthe major portion of the coating composition. With increasing amounts ofthe terpolymer in a coating composition, the gloss level and printingquality of the final dried coating increases.

The new terpolymer can be prepared as an aqueous emulsion and added inthat form directly to other ingredidents of a paper coating composition.It can be used as the only pigmentary component of the coatingcomposition or it can be used with conventional coating pigments, such3,760,151 Patented Oct. 16, 1973 as clay and titanium dioxide. In eithercase, the total pigment content in the coating formulation is largerthan the content of the paper coating binder.

The terpolymers of this invention comprise, by weight, at least about70% styrene, with the remaining 30% comprised of acrylonitrile andanother acrylic material. While styrene is believed to be the primarygloss-developing component of the terpolymers, the unique properties ofstability and high gloss, as compared to conventional poly-styrenehomopolymers, are the result of the novel combination of the threemonomers making up the terpolymers. Preferably, the terpolymerscomprise, by weight, about 70 to styrene monomer, about 8 to 25%acrylonitrile, and about 0.5 to 5% of a material selected from the groupconsisting of acrylamide, acrylic acid, and methacrylic acid. In thepreferred embodiments of the invention, acrylamide is used.

The preferred method of preparing one of the novel terpolymers is toprepare it as an aqueous emulsion by emulsion polymerization. In makinglatex emulsion conventionally, protective colloids, such as gum Arabic,carboxymethylcellulose, casein, alpha protein, and polyvinyl alcohol,are used to provide chemical and mechanical stability to the latexemulsion. Without their use, a latex emulsion would tend to gel underend-use conditions, as may occur when used in paper coatingcompositions. Additionally, anti-freeze compounds are added to theemulsion to provide freeze-thaw stability. I have found, however, that astable emulsion of the novel terpolymer can be prepared without use ofconventional protective colloids and anti-freeze compounds by properchoice of emulsifiers and temperature during the emulsionpolymerization. In this connection, primary emulsifiers, those usedduring the polymerization, are employed. The preferrcd primaryemulsifiers are a mixture of anionic and non-ionic compounds, the ratioof anionic to non-ionic being about 1:1 to 2:1. Below this ratio, thelatex tends to be unstable because the particle size of the terpolymerbecomes too large. Above this ratio, the particle size of the terpolymerbecomes too small for optimum mechanical stability and for optimumgloss-producing ability in paper coatings. The preferred non-ionicprimary emulsifiers are alkyl aryl polyoxyethylene ethanols having about10 to 70 ethylene oxide units, used in an amount of about 1.0 to 3.0% ofthe total weight of monomers. For example, such non-ionic emulsifiersare octyl phenoxy ethanol having about 40 ethylene oxide groups, nonylphenoxyethylene ethanol having about 30 ethylene oxide groups, andisooctyl phenyl polyoxyethylene ethanol.

The preferred anionic emulsifiers are used in an amount of about 1.5 to5.0% of the total weight of monomers and are selected from the groupconsisting of alkyl aryl sulfonates, such as for example sodium dodecylbenzene sulfonate, and triethanolamine dodecyl benzene sulfonate; alkylaryl polyoxyethylene sulfates, such as for example the well-known,commercially available compounds sold under the trade names Triton W-30,Triton X-301, and Triton 770; and alkyl aryl polyoxyethylene sulfonates,such as for example sodium octyl benzylpolyoxyethylene sulfonate (TritonX-200 or Triton X-202).

If the terpolymer is to be used as an organic pigment in paper coatingcompositions, the use of secondary emulsifiers, those used after thepolymerization reaction is completed, is desirable. It has been foundthat multi-valent ions commonly found as impurities in conventionalcoating clays tend to gel a latex emulsion. To this end and to providethe terpolymer emulsions of this invention with chemical stability,secondary emulsifiers are added to the products of the emulsionpolymerization reaction when the end-use of the terpolymer is as acoating pigment. The preferred secondary emulsifiers are again a mixtureof anionic and non-ionic compounds. The preferred non-ionic secondaryemulsifiers are selected from alkyl aryl polyoxyethylene ethanols havingabout to 70 ethylene oxide groups, such as for example those set forthabove in connection with the non-ionic primary emulsifiers. Thepreferred anionic secondary emulsifiers are selected from alkyl arylpolyoxyethylene sulfonates, such as for example those set forth above inconnection with the anionic primary emulsifiers. The anionic emulsifieris added in an amount varying from about 0.8 to 2.0% by weight of thetotal amount of monomers. The non-ionic emulsifier is added in an amountvarying from about 1.0 to 5.0 parts by weight of the total amount ofmonomers. The ratio of anionic to non-ionic compound is not critical inconnection with the secondary emulsifiers. It is preferred, however,that the overall ratio of anionic to non-ionic compounds used as primaryand secondary emulsifiers range from about 1 to 0.85 to about 1 to 1.2to insure chemical stability of the terpolymer emulsion when used inpaper coating compositions.

To prepare an aqueous emulsion of the new terpolymer, a reactor is firstcharged with water and the temperature is raised to reaction temperatureof about 65 to 70 C. The use of an accelerator is optional and if one isused, it is preferably charged with the water. Such materials arewell-known in the art and may be, for example, sodium bisulfite, sodiumthiosulfate, sodium metabisulfite, or sodium bicarbonate. A nitrogenblanket is introduced. Then, with constant agitation, the primaryemulsifiers and reaction catalyst are added as one mixturesimultaneously with a separate mixture of the three monomers. Theseadditions are preferably made at a constant ratio of the mixture of themonomers to the emulsifier-catalyst mixture in order to insure uniformparticle size of the resulting terpolymers. When the addition of theseingredients is completed, additional catalyst may be added, and thereaction mixture is maintained at about 80 to 95 C. for about one hourto complete the reaction. The use of an addition catalyst is optionaland may be used to insure that all monomers have reacted, in order toavoid any odor attendant with unreacted monomer. In an end-use whereodor is no problem, an addition catalyst is unnecessary since the yieldsof terpolymer are quite high.

If secondary emulsifiers are used, they may be added to the reactionvessel immediately before the temperature of the reaction is raised to80 to 95 C. or they may be added after this heating period. Thepreferred procedure is to add the secondary emulsifiers after theheating period, before the terpolymer emulsion has cooled to roomtemperature. In any event, with or without the secondary emulsifiers,the resulting aqueous emulsion of terpolymer is mechanically stable andready for shipment, use, or storage.

The rate of agitation of the reaction mixture bears on the finalparticle size of the terpolymer. The rate of agitation is set to yieldan average particle size in the range from about 0.1 to 0.2 micron, witha preferred range from about 0.12 to 0.17 micron for best mechanicalstability of the aqueous emulsion and gloss-producing ability of theterpolymer when used in a paper coating composition. The preferred rateof stirring with an impeller type of agitator is about 260 to 350r.p.m., but the rate may change as reaction vessel and stirrer sizeschange.

The reaction and addition catalysts can be any of the variouswater-soluble per compounds known in the art, for example, hydrogenperoxide in its free state as a solution in water or in a dry statebound to an inorganic salt, such as the perborates, or bound to organicmaterials, such as urea, or other free-radical generatin reagents suchas persulfates, percarbonates, and persilicates. The preferred reactioncatalysts are potassium. persulfate and ammonium persulfate. Thepreferred addition catalyst, when used, is t-butyl hydroperoxide, butothers may be used. The amount of reaction catalyst used usually variesbetween about 0.1 and 1.0% by weight of the total content of monomers,and the amount of addition catalyst, when used, varies between about0.05 and 0.5% on the same weight basis.

The stability of the terpolymer emulsion, in the absence of conventionalprotective colloids, is believed to be due to the use of bulkyemulsifiers which perform as emulsifiers and as chemical and mechanicalstabilizers for the emulsion. Preferably, the total amount of primaryand secondary emulsifiers do not exceed about 5.8% by weight of thetotal weight of monomers.

Stable emulsions of the terpolymers have been prepared wherein theemulsion has a terpolymer to water ratio by weight ranging from about35:65 to about 50:50.

DETAILED DESCRIPTION The invention will be described in greater detailwith the aid of the following examples, which are given in illustrationof the invention but are not intended as limitations thereon. Whereparts are mentioned, they are parts by weight unless otherwisespecified.

EXAMPLE 1 A stable aqueous emulsion of a terpolymer was preparedaccording to the following formulation:

Octyl phenoxy ethanol (40 polyoxyethylene units) 10 Secondaryemulsifiers:

Sodium octyl benzylpolyoxyethylene sulfonate 6.4 Octyl phenoxy ethanol(40 polyoxyethylene units) 13.6 Water 1000 A reaction vessel was chargedwith the water and 0.4 part of sodium bisulfite, the vessel was purgedwith nitrogen and sealed, and the temperature of the water was raised toabout 67.5 C. Constant agitation with an impeller type of stirrer drivenat about 300 r.p.m. was maintained throughout the complete processdescribed below. The styrene, acrylonitrile, and acrylamide monomers,previously mixed together, were then added to the reaction vessel over aperiod of about minutes. This time normally varies between about 1 and 2hours. Simultaneously, with the addition of the monomers, the primaryemulsifiers and potassium persulfate, previously dissolved together insufiicient water to make a total of about parts solution, were added tothe reaction vessel at a rate of about 1 part, by volume, to 5 parts ofthe mixture of monomers. The temperature throughout these additions wasmaintained between about 65 to 70 C. When the additions of monomers,primary emulsifiers, and reaction catalyst were completed, the additioncatalyst, t-butyl hydroperoxide, was added and the temperature of thereaction mixture was raised to about 85 C. and maintained for about 1hour. After cooling the reaction mixture to about 50 C., the secondaryemulsifiers were added and agitation continued for about 15 minutes,after which the reaction products were cooled to room temperature.

Analysis of the resulting aqueous emulsion of thesyrene-acrylonitrile-acrylamide terpolymer showed that all of themonomers had been reacted. The terpolymer comprised, by weight, about81% styrene, about 18% acrylonitrile, and about 1% acrylamide. The pH ofthe emulsion was about 3.0, and the solids content was about 42% Theemulsion exhibited excellent mechanical, chemical, and freeze-thawstability. In runs similar to the above, but without the addition of thesecondary emulsifiers, the resulting emulsions still exhibited excellentmechanical stability, being able to withstand vigorous agitation (12,000rpm.) for more than 30 minutes before the breakdown of the emulsions.

EXAMPLES 2 AND 3 The process described in Example 1 was repeated exceptthat in Example 2 acrylic acid was substituted for acrylamide, and inExample 3 methacrylic acid was substituted for acrylamide. Thesubstitutions were on a direct basis by Weight. In each case, stableaqueous emulsions of a terpolymer were prepared. In Example 2, theterpolymer comprised, by weight, about 81% styrene, about 18%acrylonitrile, and about 1% acrylic acid. In Example 3, the compositionof the terpolymer was similar except that it comprised about 1%methacrylic acid in place of the acrylic acid.

EXAMPLE 4 Example 1 was repeated, except that the parts of the monomersused were as follows: styrene, 696 parts; acrylonitrile, 96 parts; andacrylamide, 8 parts. The resulting stable emulsion contained aterpolymer comprising by weight about 87% styrene, about 12%acrylonitrile, and about 1% acrylamide.

EXAMPLE 5 Example 3 was repeated, except that the parts of the monomersused were as follows: styrene, 600 parts; acrylonitrile, 160 parts; andmethacrylic acid, 40 parts. The resulting stable emulsion contained aterpolymer comprising, by weight, about 75% styrene, about 20%acrylonitrile, and about 5% methacrylic acid.

In the above examples, the average particle diameters of the terpolymersin the emulsions ranged from about 0.1 to 0.2 micron. The preferredparticle size range for a terpolymer destined for use as a pigment in apaper coating composition has been found to be about 0.12 to 0.17micron.

EXAMPLE 6 A coating composition for paper was prepared by dispersing inwater about 25 parts butadiene-styrene latex and about 239 parts of theterpolymer emulsion from Example 1 (pH adjusted to about 8.0 withammonium hydroxide), to give a coating composition having a solidscontent of about 40%, all parts being by weight. On a dry basis, thecoating composition contained about parts of the terpolymer preparedaccording to Example 1. The coating composition was applied to atraveling Web of paper by a trailing blade coater to give a coat weightof about 6. 4 pounds per 3000 sq. ft. of paper, and the web was dried.There were no runnability problems. After gloss-calendering, theresulting coated paper had a B & L gloss of about 75 and an LRLbrightness of about 83.

In this example, the terpolymer was the only pigmentary component of thecoating composition and functioned as a gloss-producing organic pigment.Subsequent examples Will compare the gloss-producing ability of theterpolymer with a conventional homopolymer.

EXAMPLE 7 The terpolymers of this invention can be used withconventional paper coating pigments in coating compositions. Forexample, a coating composition for paperboard was prepared by dispersingin water about 100 parts coating clay, about 24 parts of the terpolymeremulsion from Example 1 (about 10 parts terpolymer, dry basis), and asbinder about parts polyvinyl acetate and 2 parts alpha protein, allparts being by weight, to give a coating composition having a solidscontent of about 60%. The coating composition was applied by a bladecoater to a traveling web of 18 point paperboard to give a coat weightof about 7 pounds per 3300 sq. ft. of paperboard. After drying, thecoated paperboard was gloss-calendered with one nip heated to about 325F., the calender loading being about 250 p.l.i.

EXAMPLES 8ll B dz L gloss LRL brightness K&Nink

Wax holdout pick Example wuwsvrvv E E-H5 5 accountscan-- qonqoooo Bycomparing Examples 7 and 10, it can be seen that the new terpolymerperformed much better than the homopolymer as a gloss-developing organicpigment, had significantly better ink holdout properties (after 15minutes testing), and provided substantially equivalent brightness andwax pick.

EXAMPLES 12-13 The terpolymers of this invention perform Well aspigments in coating compositions for paper. In Example 12, a coatingcomposition was prepared by dispersing in water about parts clay, about5.5 parts of the terpolymer from Example 1 (dry basis), and as binderabout 10 parts starch and 10 parts of a conventional styrene-butadienelatex, with parts by weight, to give a coating composition having asolids content of about 62%. The coating composition was applied by ablade coater to a traveling web of paper at a coat weight of about 10pounds per 3000 sq. ft. of paper. After drying, the coated paper wassupercalendered with four nips, the loading being about 180 p.l.i. atthe bottom nip.

In Example 13, the above was repeated, except that a polystyrenehomopolymer replaced, on an equal basis, the new terpolymer madeaccording to Example 1. The properties of the coated papers were asfollows:

emulsions of the novel terpolymers can be prepared, and the emulsionscan be added directly to other paper coating ingredients to form coatingcompositions which yield improvements in gloss over the level providedby conventional binder latices and styrene homopolymer latices. Aspreviously stated, the addition of secondary emulsifiers to theemulsions is preferred when the terpolymers are intended for use inpaper coating compositions. This is done to prevent any tendency of theemulsion to gel in the presence of contaminants that might be present inthe other coating components. However, the terpolymers of this inventionfind utility in other areas where there is no need for the secondaryemulsifiers. Such would be the case when the terpolymers are used infloor polishes to replace the polystyrene emulsions conventionally used.

7 8 It is obvious that many variations may be made in the Referenc Citedproducts and processes of this invention without depart- UNITED STATESPATENTS ing from the spirit and scope thereof.

1 i 2,772,252 11/1956 Brlsltln et a1 26080.5 1. A terpolymer comprisingstyrene, acrylonitrile and 5 3,053,819 9/ 9 2 Ca lln 26080.5

acrylamide, wherein the components of the terpolymer are present byweight according to the following: about JOSEPH SCHOFER Pnmary Exammer70 to 90% styrene, about 8 to 25% acrylonitrile, and S M LEVIN, A i t tE i about 0.5 to 5% acrylarnide.

2. A terpolymer according to claim 1 wherein the ter- 10 polymercomprises about 81% styrene, about 18% acrylo- 26029.6 TA, 80.8 nitrile,and about 1% acrylamide.

